JP2009503270A - Use of NF3 to remove surface deposits - Google Patents

Abstract

The present invention relates to an improved remote plasma cleaning method for removing surface deposits from a surface, such as the interior of a process chamber used to manufacture electronic devices. The improvement includes the use of a high neutral temperature activation gas of at least about 3000 K and the addition of an oxygen source to the NF ₃ cleaning gas mixture to improve the etch rate.

Description

The present invention relates to a method for removing surface deposits by using an activated gas mixture produced by remotely activating a gas mixture comprising an oxygen source and NF ₃ . More specifically, the present invention relates to surface deposits from the inside of a chemical vapor deposition chamber by using an activated gas mixture produced by remotely activating a gas mixture comprising an oxygen source and NF ₃ . It is related with the removal method.

  Chemical vapor deposition (CVD) and plasma enhanced chemical vapor deposition (PECVD) chambers in the semiconductor processing industry require regular cleaning. Popular cleaning methods include in situ plasma cleaning and remote chamber plasma cleaning.

  In the in-situ plasma cleaning method, the cleaning gas mixture is activated to plasma in the CVD / PECVD process chamber to clean the deposits in situ. There are several deficiencies in the in-situ plasma cleaning method. First, chamber parts that are not directly exposed to the plasma cannot be cleaned. Secondly, cleaning methods include ion bombardment induced reactions and spontaneous chemical reactions. Since ion bombardment sputtering erodes the surface of the chamber parts, expensive and time consuming part replacement is required.

  Understanding the shortcomings of in-situ plasma cleaning, remote chamber plasma cleaning methods are becoming more popular. In the remote chamber plasma cleaning method, the cleaning gas mixture is activated by the plasma in a separate chamber other than the CVD / PECVD process chamber. The plasma neutral product then passes from the light source chamber to the interior of the CVD / PECVD process chamber. The transfer path may consist, for example, of a short connecting tube and a showerhead of a CVD / PECVD process chamber. In contrast to in situ plasma cleaning methods, remote chamber plasma cleaning methods involve only spontaneous chemical reactions, thus avoiding erosion problems caused by ion bombardment in the process chamber.

  Capacitively coupled and inductively coupled radio frequency (RF) as well as microwave remote sources have been developed as power sources for remote chamber plasma cleaning methods, but the industry has found that the plasma has a toroidal configuration and is a two-way transformer. It is rapidly moving towards an inductively coupled source-coupled transformer that acts as the next side. The use of lower frequency RF power allows the use of a magnetic core that enhances inductive coupling relative to capacitive coupling, thereby reducing the energy to the plasma without excessive ion bombardment that limits the lifetime inside the remote plasma source chamber. Enable efficient migration.

NF ₃ , fluorocarbon, SF _{6 and the} like have been used as cleaning gases in the plasma cleaning method. Of these, NF ₃ is particularly attractive because of its relatively weak nitrogen-fluorine bond. NF ₃ dissociates easily and does not generate greenhouse gas emissions. It is necessary to use NF ₃ effectively as a cleaning gas.

B. B. Bai, H.C. H. Sawin, Journal of Vacuum Science & Technology A 22 (5) (2004), 2014

The present invention is a method for removing surface deposits comprising: (a) providing a gas mixture comprising an oxygen source and NF ₃ with sufficient power so that the gas mixture reaches a neutral temperature of at least about 3,000 K; Activating in a remote chamber for a period of time to form an activated gas mixture, and then (b) contacting the activated gas mixture with a surface deposit, thereby at least a portion of the surface deposit And a step of removing.

The surface deposits removed in the present invention include those materials generally deposited by chemical vapor deposition or plasma enhanced chemical vapor deposition or similar methods. Such materials include silicon, doped silicon, silicon nitride, tungsten, silicon dioxide, silicon oxynitride, silicon carbide, SiBN, FSG (fluorosilicate glass), silicon carbide, and Black Diamond (Applied Material). Low (such as Applied Materials), Coral (Novellus Systems) and Aurora (ASM International), including SiC _x O _x H _x or PECVD OSG Various silicon oxygen compounds called K materials are included. A preferred surface deposit in the present invention is silicon nitride.

  One embodiment of the present invention is the removal of surface deposits from the interior of a process chamber used to manufacture electronic devices. Such a process chamber could be a chemical vapor deposition (CVD) chamber or a plasma enhanced chemical vapor deposition (PECVD) chamber.

  Other embodiments of the present invention include, but are not limited to, removal of surface deposits from the metal, cleaning of the plasma etch chamber and stripping of the photoresist.

  The method of the present invention includes an activation step in which the cleaning gas mixture is activated in a remote chamber. Activation may be performed by any means that allows the dissociation of most of the feed gas to be achieved, such as radio frequency (RF) energy, direct current (DC) energy, laser irradiation and microwave energy. One embodiment of the present invention is the use of an inductively coupled low frequency RF power coupled transformer where the plasma has a toroidal configuration and acts as the secondary side of the transformer. The use of lower frequency RF power allows the use of a magnetic core that enhances inductive coupling relative to capacitive coupling, thereby reducing the energy to the plasma without excessive ion bombardment that limits the lifetime inside the remote plasma source chamber. Enable efficient migration. Typical RF power used in the present invention has a frequency lower than 1,000 KHz. Another embodiment of the power source in the present invention is a remote microwave, inductively coupled or capacitively coupled plasma source.

  The activation of the present invention uses sufficient power for a sufficient time to form an activated gas mixture having a neutral temperature of at least about 3,000 K. The neutral temperature of the resulting plasma depends on the power and residence time of the gas mixture in the remote chamber. Under certain power inputs and conditions, the neutral temperature will increase with increasing residence time. In the present invention, the preferred neutral temperature of the activated gas mixture is greater than about 3,000K. Under appropriate conditions (considering power, gas composition, gas pressure and gas residence time), a neutral temperature of at least about 6000 K may be achieved.

The activation gas is formed in a separate remote chamber that is external to the process chamber but near the process chamber. In the present invention, a remote chamber means a chamber where plasma is generated, and a process chamber means a chamber where surface deposits are deposited. The remote chamber is coupled to the process chamber by any means that allows movement of the activation gas from the remote chamber to the process chamber. For example, the transfer path may consist of a short connecting tube and a CVD / PECVD process chamber showerhead. The remote chamber and the means for connecting the remote chamber with the process chamber are constructed of materials known in the art that can contain an activated gas mixture. For example, aluminum and cathodic aluminum oxide are commonly used for chamber components. Al ₂ O ₃ may be coated on the inner surface to reduce surface recombination.

The gas mixture that is activated to form the activated gas includes an oxygen source and NF ₃ . The “oxygen source” of the present invention refers herein to a gas capable of generating atomic oxygen in the activation step of the present invention. Here, examples of the oxygen source include, but are not limited to, O ₂ and nitrogen oxides. The nitrogen oxide of the present invention refers herein to a molecule consisting of nitrogen and oxygen. Examples of nitrogen oxides include, but are not limited to NO, N ₂ O, NO ₂ . A preferred oxygen source is oxygen gas.

  The gas mixture that is activated to form the activated gas may further comprise a carrier gas such as argon, nitrogen and helium.

  The total pressure in the remote chamber during the activation process may be from about 0.1 torr to about 20 torr.

It has been found in the present invention that an oxygen source can dramatically increase the etch rate of NF ₃ into silicon nitride. In one embodiment of the present invention, as shown in Example 1 below, a small amount of oxygen gas addition can increase the etch rate of the NF ₃ / Ar cleaning gas mixture to silicon nitride by a factor of four.

  The following examples are intended to illustrate the invention and not to limit it.

FIG. 1 shows a schematic diagram of a remote plasma source, transport tube, process chamber and exhaust system used in the present invention. The remote plasma source is a commercial toroidal MKS Astron (R) ex reactive gas generator device manufactured by MKS Instruments, Andover, Massachusetts, USA. A feed gas (eg, oxygen, NF ₃ , argon) was introduced into the remote plasma source from the left and passed through a toroidal discharge where they were discharged with 400 KHz radio frequency power to form an activated gas mixture. Oxygen is produced by Airgas with 99.999% purity. NF ₃ gas is manufactured by the present applicant with 99.999% purity. Argon is manufactured by air gas with a grade of 5.0. The activated gas mixture then passed through an aluminum water cooled heat exchanger to reduce the heat load of the aluminum process chamber. The surface deposit-coated wafer was placed on a temperature-controlled mount in the process chamber. Neutral temperature is measured by emission spectroscopy (OES), in which rotational vibrational transition bands of diatomic species such as C ₂ and N ₂ are theoretically fit to provide neutral temperature . See also (Non-Patent Document 1), which is incorporated herein by reference. The etching rate of the surface deposit by the activated gas is measured by an interferometry apparatus in the process chamber. N ₂ gas is added at the inlet of the exhaust pump both to dilute the product to a concentration appropriate for FTIR measurement and to reduce product hang-up in the pump. The concentration of chemical species in the pump exhaust gas was measured using FTIR.

Example 1
This example demonstrated the effect of oxygen source addition on the silicon nitride etch of the NF ₃ / Ar system. The results are also shown in FIG. In this experiment, the feed gas consisted of NF ₃ , Ar, and optionally O _{2 with} an NF ₃ flow rate of 1333 sccm and an Ar flow rate of 2667 sccm. The chamber pressure was 2 torr. The feed gas was activated to a neutral temperature higher than 3000 K with 400 KHz 4.6 Kw RF power. The activation gas then entered the process chamber and etched the silicon nitride surface deposits on a mount adjusted to a temperature of 50 ° C. When there was no oxygen source in the feed gas, ie the feed gas mixture consisted of 1333 sccm NF ₃ and 2667 sccm Ar, the etch rate was only 500 liters / minute. As shown in FIG. 2, when 100 sccm of O ₂ was added to the feed gas mixture, ie, the feed gas mixture consisted of 100 sccm O ₂ , 1333 sccm NF ₃ and 2667 sccm Ar, the silicon nitride etch rate was It increased from 500 to 1650 liters / minute. When 200 sccm O ₂ was added to the feed gas mixture, ie the feed gas mixture consisted of 200 sccm O ₂ , 1333 sccm NF ₃ and 2667 sccm Ar, the etch rate further increased to 2000 さ ら に / min.

(Example 2)
This example showed the silicon dioxide etch rate of the NF ₃ / O ₂ / Ar system. The NF ₃ flow rate was adjusted to 1333 sccm, the Ar flow rate was 2667 sccm, and the O ₂ flow rates were 0, 100, 300, 500, 700, and 900 sccm, respectively. It has been found that oxygen addition does not significantly affect the silicon dioxide etch rate of the NF ₃ / Ar system. In this experiment, the chamber pressure was 2 torr. The feed gas was activated to a neutral temperature higher than 3000 K with 400 KHz 4.6 Kw RF power. The activated gas then entered the process chamber and etched the silicon dioxide surface deposits on a mount adjusted to a temperature of 100 ° C. The etching rate is shown in FIG.

1 is a schematic illustration of an apparatus useful for carrying out the method. FIG. 5 is a plot of the effect on etch rate to silicon nitride with O ₂ addition to an NF ₃ + Ar feed gas mixture. FIG. 5 is a plot of the effect on etch rate on silicon dioxide with O ₂ addition to an NF ₃ + Ar feed gas mixture.

Claims (14)

A method for removing surface deposits,
(A) activating a gas mixture comprising an oxygen source and NF ₃ by activating in a remote chamber using sufficient power for a sufficient time such that said gas mixture reaches a neutral temperature of at least about 3,000 K; Forming a activated gas mixture; and thereafter (b) contacting the activated gas mixture with a surface deposit, thereby removing at least a portion of the surface deposit.   The method of claim 1, wherein the surface deposit is removed from within a process chamber used to manufacture an electronic device.   The method according to claim 1, wherein the oxygen source is oxygen gas or nitrogen oxides.   The method of claim 3, wherein the oxygen source is oxygen gas.   The surface deposit is selected from the group consisting of various silicon oxygen compounds called silicon, doped silicon, silicon nitride, tungsten, silicon dioxide, silicon oxynitride, silicon carbide and low K materials. The method according to 1.   The method of claim 5, wherein the surface deposit is silicon nitride.   The method of claim 1, wherein the power is generated by an RF source, a DC source, or a microwave source.   The method of claim 7, wherein the power is generated by an RF source.   9. The method of claim 8, wherein the activated gas mixture in the remote chamber forms a toroidal configuration and the RF power is an inductively coupled transformer having a frequency lower than 1,000 KHz.   The method of claim 9, wherein at least one magnetic core is used to enhance the inductive coupling.   The method of claim 1, wherein the pressure in the remote chamber is 0.1 to 20 torr.   The method of claim 1, wherein the gas mixture further comprises a carrier gas.   13. The method of claim 12, wherein the carrier gas is at least one gas selected from the group of gases consisting of nitrogen, argon and helium.   14. The method of claim 13, wherein the carrier gas is argon, helium or a mixture thereof.

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